Object reference not set to an instance of an object.

[alain250sxf]

I got this error from this code:

ERROR:
An unhandled exception of type 'System.NullReferenceException' occurred in Lap Time Analyser.exe

Additional information: Object reference not set to an instance of an object.

CODE:

Private Sub btnplusminus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnplusminus.Click
        Dim laptime() As String
        Dim i, num As Integer
        Dim sr As IO.StreamReader = IO.File.OpenText(path)
        Do While (sr.Peek <> -1)
            sr.ReadLine()
            num += 1
        Loop
        sr.Close()
        Dim srr As IO.StreamReader = IO.File.OpenText(path)
        For i = 1 To num
            laptime(i) = srr.ReadLine
        Next
        srr.Close()
    End Sub

Im thinking its the laptime(i) that is screwing up because that is where it stops in the debugging tool. Help PLZ

My file looks like :

Alain
Ste-Julie
03
02
21
4/18/2006 5:25:14 PM

[|2eM!x]

You need to put a new before io.streamreader to actually create the streamreader

[alain250sxf]

How would I do that? Whats the code? I dont know where exactly to put it.

[|2eM!x]

Dim sr As New IO.StreamReader(path)

Like that

[Kasracer]

Whats the code?

new

I dont know where exactly to put it.

put a new before io.streamreader

|2eM!x already answered your questions

[alain250sxf]

That didnt fix the bug.
It still says:
An unhandled exception of type 'System.NullReferenceException' occurred in Lap Time Analyser.exe

Additional information: Object reference not set to an instance of an object.

And if I put the array (laptime()) as double is says :
An unhandled exception of type 'System.InvalidCastException' occurred in microsoft.visualbasic.dll

Additional information: Cast from string "Alain " to type 'Double' is not valid.

It has something to do with the array. I just dont know what.

My code now looks like :

Private Sub btnplusminus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnplusminus.Click
        Dim laptime() As Double
        Dim i, num As Integer
        Dim sr As IO.StreamReader = IO.File.OpenText(path)
        Do While (sr.Peek <> -1)
            sr.ReadLine()
            num += 1
        Loop
        sr.Close()
        PlusMinus(laptime, i, num)
 
    End Sub
    Private Sub PlusMinus(ByRef laptime() As Double, ByRef i As Integer, ByRef num As Integer)
 
        Dim sr As New IO.StreamReader(path)
        For i = 1 To num
            laptime(i) = (sr.ReadLine)
        Next
        sr.Close()
 
    End Sub

[jmcilhinney]

Actually, I think you'll find that it has nothing to do with the StreamReader. File.OpenText returns a StreamReader object, so while Remix's code is not incorrect, it is not necessary in this case.

The problem is the fact that you haven't created an array. This line:

Dim laptime() As String

does NOT create an array object. It declares an array variable, but that variable does not refer to an object. You have to specify the upper bound to actually create an array object. Arrays are fixed-size so one cannot possibly be created if you haven't specified that size in the first place. That all means that this line:

laptime(i) = srr.ReadLine

is attempting to set an element that doesn't exist in an array that doesn't exist. You're reading the entire file twice. The first time you're getting the number of lines so you could use that to create the array, but that is incredibly inefficient. What if you have thousands of lines? Do you really want to read them all just to get the number and then read them all again? If you want to use an array-like object that can be resized dynamically then you should use a collection. Because you are storing strings the obvious choice is the StringCollection. You could change this:

Dim laptime() As String
        Dim i, num As Integer
        Dim sr As IO.StreamReader = IO.File.OpenText(path)
        Do While (sr.Peek <> -1)
            sr.ReadLine()
            num += 1
        Loop
        sr.Close()
        Dim srr As IO.StreamReader = IO.File.OpenText(path)
        For i = 1 To num
            laptime(i) = srr.ReadLine
        Next

to this:

Dim lapTimes As New Specialized.StringCollection
 
        Dim sr As IO.StreamReader = IO.File.OpenText(path)
 
        Do Until sr.Peek = -1
            lapTimes.Add(sr.ReadLine())
        Loop
 
        sr.Close()

There are even easier ways to go about this though. You haven't specified what version of VB you're using (*sigh*) so I'll give you code for both.

2003:

Dim sr As IO.StreamReader = IO.File.OpenText(path)
        Dim lapTimes As String() = System.Text.RegularExpressions.Regex.Split(sr.ReadToEnd(), Environment.NewLine)
 
        sr.Close()

2005:

Dim lapTimes As String() = My.Computer.FileSystem.ReadAllText(path).Split(New String() {Environment.NewLine}, StringSplitOptions.None)

There you go. One line in VB 2005 and three lines in earlier versions.

[alain250sxf]

ok...i kinda understand how that works. But I dont see how I can assign my arrays. Like, laptimes(i) = sr.readline, I only want it to ride the 3 lines with numbers in the txt file:

Alain
Ste-Julie
03
43
40
4/20/2006 12:33:55 AM

Alain
Ste-Julie
02
32
40
4/20/2006 12:34:00 AM

Private Sub btnplusminus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnplusminus.Click
        Dim i, num As Integer
        Dim sr As IO.StreamReader = IO.File.OpenText(path)
        Dim laptimes As String() = System.Text.RegularExpressions.Regex.Split(sr.ReadToEnd(), Environment.NewLine)
 
        Do While (sr.Peek <> -1)
            sr.ReadLine()
            num += 1
        Loop
        sr.Close()
        Dim srr As New IO.StreamReader(path)
        For i = 1 To num
            laptimes(i) = (srr.ReadLine)
        Next
        srr.Close()
    End Sub

Version 2003

[jmcilhinney]

Calling ReadToEnd reads the entire file and returns an single String. Once you've done that Peek will return -1 so your loops are useless. A StreamReader can only move forward. Once it reaches the end of the file that's it. If you want to treat different lines in your file in different ways then you're going to need to do more work. Think about waht you would do if you were reading it with your eyes and using a pen and paper. You would read the file in blocks of five lines and you'd treat each of those five lines in a different way. That's what you'll need to do in your code. You can either process the lines as you read them or else read the entire file and then process the lines from your array.

[alain250sxf]

But I dont get why my old code (the first one I posted) doesnt work. Doesnt it make sense? Everything works fine until it gets to the laptime(i) part. I've seen that

For i = 1 To num 
laptimes(i) = sr.ReaLine
lstreport.Items.Add(laptimes(i))
Next

work before. So why doesnt it work NOW?!

[jmcilhinney]

This line:

Dim laptimes As String() = System.Text.RegularExpressions.Regex.Split(sr.ReadToEnd(), Environment.NewLine)

reads the entire file into a single string, splits that string on the line breaks and returns an array where each element is a line from the file. Why do you now want to go back and read the file again? There is no point because you already have its entire contents. Appart from that, the code you're using won't read it anyway. The contents of your Do loop will not get executed because Peek will return -1 immediately for the very reason Iposted previously: ReadToEnd reads the entire file and so the StreamReader will be at the end of the file afterwards. Because your Do loop isn't executed your 'num' variable is zero so your For loop will begave very differently to what you expect. It will read the first line of the file into the second element of the array, then read the second line into the first element of the array and then exit. Like I said, raeding the file again is COMPLETELY pointless because you already have the entire contents. Also, arrays are zero-based, which means that their indexes go from 0 to (Length - 1), not 1 to Length. You should read the section about arrays in the Start VB.NET tutorial in my signature because your understanding of how they behave in VB.NET is lacking.

You should also familiarise yourself with with the capabilities of the debugger. Yopu should have set a breakpoint at the top of that code and stepped through it line by line. You could then follow the values of any variable, property or expression at each line so you can see exactly what your code is doing.